In general with automotive internal combustion engines (see for example the disclosure of Japanese Unexamined Patent Publication No. 63-179150) a mechanism is provided for shutting off the fuel supply in a predetermined deceleration condition.
With initial designs, the fuel supply is timed to be shut off immediately after satisfying conditions such as, the rate of reduction in throttle valve opening exceeds a predetermined value, and the engine rotational speed at the start of the deceleration operation exceeds a predetermined value.
In reality however, a delay occurs from the start of the deceleration operation until the engine output torque is reduced and the reduction in torque transmitted to the axle through the transmission to give an actual reduction in the vehicle speed. Therefore, if the fuel supply to all of the cylinders is shut off immediately after the deceleration operation, then this will give a large deceleration resistance while the travelling inertia of the vehicle is still large, resulting in a large torque shock with deterioration in comfortable ride.
It has thus been considered to shut off the fuel supply after a predetermined time lapse from commencement of the deceleration operation. Also, since an excessive torque change results when the fuel supply is shut off to all cylinders simultaneously, then a general stepwise fuel supply shut off control has been proposed to give stepwise reduction in the torque. This involves first shutting off the fuel supply to some cylinders after the deceleration operation and then shutting off the fuel supply to the remaining cylinders. With this arrangement however, the timing for the fuel supply shut off to some or all of the cylinders is set according to an elapsed time after the deceleration operation.
With the system wherein the timing to reduce the torque is merely set according to an elapsed time after the deceleration operation, it is not possible to shut off the fuel supply with good timing. This is because deceleration conditions differ due to such factors as the engine operating conditions at the time of or after the deceleration operation, and the travelling road surface conditions. This results in problems such as excessive torque fluctuations which detract from comfortable ride, and the negation of any sufficient improvement in fuel consumption due to the delay in supply shut off.
In view of the above heretofore encountered problems, it is a first object of the present invention to provide a method for controlling the fuel supply shut off of an internal combustion engine which sufficiently improves fuel consumption and comfortable ride, by controlling the fuel supply shut off on the basis of actual vehicle deceleration conditions.
Moreover, it is a second object of the present invention to provide an apparatus for controlling the fuel supply shut off of an internal combustion engine which sufficiently improves fuel consumption and comfortable ride, by controlling the fuel supply shut off on the basis of actual vehicle deceleration conditions.